There are some quirks in the Amazon way of doing things, The more items you order in a order the odds increase proportionately that you will not get that order in two days if Amazon decides to ship them all in one package . A lot of times if you order two items, one item will be at one facility and the other item will be at another facility and alot of times they will ship the one of those two items to the nearest facility to combine them before packaging them up and shipping them from that facility.
That works the other way, too.
Friday, I ordered a CD and chose to have it shipped regular delivery (5-7 business days) instead of 2 day delivery (thus getting a $1 credit for music downloads).
Then, Saturday morning I ordered something else and chose 2 day delivery.
Amazon combined the orders and I received both of them yesterday.